A suitable application of the present invention is downhole compression of natural gas; this is done to enhance the production from an underground natural gas reservoir. Natural gas is typically produced from an underground reservoir containing natural gas through tubing arranged in a well drilled to the reservoir. During production, the cumulative amount of natural gas produced increases and consequently the reservoir pressure will decrease. As a result of the decrease in reservoir pressure, the production rate decreases and, in order to maintain the production rate at an economically acceptable level the gas has to be compressed. The compression is preferably done downhole. This compression also results in an increased economic cumulative production.
An alternative application of the present invention is compression of a gas flowing through a pipeline to increase the rate of gas transported through the pipeline.
U.S. Pat. No. 2,899,287 discloses an apparatus for producing combustible gas from fuel oil or coal comprising a conduit provided with a non-return inlet valve arranged at the upstream inlet end of the conduit, a localized ignition source arranged in the conduit downstream of the non-return inlet valve, and means for supplying continuously fuel into the conduit between the non-return inlet valve and the localized ignition source.
The known apparatus is an apparatus for partially combusting fuel to generate a combustible gas. During normal operation (a) fuel is supplied continuously into the conduit with oxidant that has entered in the conduit through the non-return valve; (b) the combustible mixture is allowed to ignite, which ignition yields a high pressure wave front closing the non-return inlet valve and pushing gas out of the outlet end of the conduit and a low pressure wave front; and (c) the non-return inlet valve is allowed to open on arrival of the low pressure wave front to allow oxidant to enter into the conduit.
In the known method the interval between two successive combustions is determined by the geometry of the conduit which may not always have the most suitable form for an optimal interval. The pressure increase for the compression stage of the known apparatus is very small, the pressure at the outlet end of the conduit is about 2 or 3% above the pressure at the inlet end. For pumping natural gas such a pressure increase for a compression stage is unacceptably small. Therefore it is an object of the present invention to provide an apparatus for compressing a gas which will give a larger pressure increase than the known apparatus.